Regulation of glycosaminoglycan synthesis by thyroid hormone in vitro

Human skin fibroblasts synthesize and accumulate glycosaminoglycans (GAG). Recently, we reported that fibroblasts incubated in thyroid hormone-deficient media accumulate more GAG than do cultures incubated in the same media enriched with 0.1 muM triiodothyronine (T(3)) (1981. Endocrinology. 108: 2397). The current study characterizes that enhanced accumulation. Confluent cultures were maintained in thyroid hormone-deficient media without or with added T(3), labeled with [(3)H]acetate and analyzed for total [(3)H]GAG and [(3)H]hyaluronic acid content. Addition of T(3) to thyroid hormone-depleted media consistently inhibited the incorporation of [(3)H]acetate into GAG by 28-60% in fibroblast cultures from four different normal human donors. Maximal inhibitory effect was observed within 3 d after hormone addition at concentrations > 1 nM. 73% of the maximal inhibitory effect was observed in the presence of physiologic concentrations of T(3) (0.16 nM total T(3) or 1.4 pM free T(3)). The following observations indicated that T(3) inhibition of [(3)H]GAG accumulation is most likely due to a decrease in GAG synthesis rather than to changes in the acetate pool or GAG degradation: (a) Addition of 0, 100, 500, and 2,500 muM unlabeled acetate progressively decreased [(3)H]acetate incorporation into GAG, up to 80%, without altering the further inhibitory effect of T(3) (35-40%); (b). A similar effect of T(3) on GAG (32% inhibition) was observed using [(3)H]glucosamine as substrate; (c) T(3) decreased hyaluronate synthetase activity by 32%; and (d) There was no effect of T(3) on GAG degradation in a pulse-chase experiment. The effect of T(3) on [(3)H]GAG accumulation appears to be quite specific, since the hormone had no effect on the incorporation of [(3)H]leucine into trichloroacetic acid-precipitable material.Thus, thyroid hormone inhibits GAG accumulation in a dose-, time-dependent, and reversible manner. This inhibition is apparently due to specific effects on the rate of macromolecular synthesis.